EMPLOYEES at Blaenavon's Big Pit were on strike on the weekend following cuts to pensions and weekend pay.
The industrial action, which is planned to take place every Saturday and Sunday afternoon until the end of August, has seen 40 workers from the museum go on strike.
The workers are members of the Public and Commercial Services Union.
The industrial action follows the decision from the National Museum Wales to cut pay for weekend work and stop the money becoming part of their pensions. Staff at the Big Pit National Coal Museum are just one of several museum sites taking industrial action. Others include St Fagans National History Museum and the National Museum, both in Cardiff.
Peter Harding, representing PCS workers at Big Pit, said: "This will affect the catering staff, the cleaners as well as us the guides. They have decided to cut from the lowest paid workers.
"Managers haven't been affected at all. Some of the cleaning staff have three jobs to make ends meet - this will be a huge loss of money to them."
Mr Harding said guides currently receive £54 for working a Sunday shift and £30 for a Saturday shift. The museum is planning to cut these payments and PCS say this will mean a loss of £3,000 to staff who work weekends.
He said: "We've had a positive reaction from the general public - it's a shame that we've had to disappoint people who wanted to visit today. What they are telling us is to do the same work but they are going to be taking money away from us -this is affecting our pensions as well."
Peter Broome, who's been a guide for the past four years, said: "We get people from all over the world coming to visit. We've just had a bus full of Americans that we've had to turn away.
"It's a shame as we want to tell them all about the history and the heritage of this place and the suffering of miners. This is not possible because of the cuts."
He added: "Saturday and Sunday shifts tend to be a lot busier. We can get around 600 people on those days."
The museum workers will be on strike on August 16, 17, 23 and 24.